Lip-smacking behavior could have an important social function among gelada monkeys.
Thore Bergman, a researcher at the University of Michigan in Ann Arbor, has discovered that monkey lip-smacking resembles human speech.
According to National Geographic, gelada monkeys reside in the high mountain meadows of Ethiopa, where they have adapted to living on steep, rocky cliffs. The 100,000 to 200,000 surviving geladas are also the last remaining species of ancient grazing primates. The rare monkeys have fatty rear ends which allow them to sit and eat grass for long periods of time.
A news release from Cell Press notes that the gelada is the only nonhuman primate that communicates with a “speech-like, undulating rhythm.” According to Bergman, the sounds that other monkeys and apes make are usually one or two syllables. The gelada’s lip-smacking vocalizations also lack quick changes in pitch and volume.
According to Bergman, the lip-smacking behavior, which is shown during friendly interactions with other geladas, could have been an evolutionary step toward human speech.
The finding offers evidence for the lip-smacking beginnings of speech because it reveals that this “evolutionary pathway is at least plausible,” noted Bergman. The finding shows that “nonhuman primates can vocalize while lip-smacking to create speech-like sounds.”
When Bergman first encountered the rare monkey’s vocal lip-smacking during field research in 2006, he had to explore his surroundings to see if another human was nearby. He called the experience “unnerving” because the monkey sound a lot like humans. He said that this was an experience he had not had around other monkeys.
Bergman has studied recordings of the geladas’ vocal lip-smacking to identify a rhythm that closely matches human speech. He discovered that the pattern of sound generated is structurally similar to human speech.
Bergman also posited that lip-smacking could serve the same purpose as language in social interactions. “Language is not just a great tool for exchanging information; it has a social function,” Bergman said. “Many verbal exchanges appear to serve a function similar to lip-smacking.”
Lip-smacking behavior could have an important social function among gelada monkeys. National Geographic points out that gelada family units frequently come together to create large foraging bands of 30 to 350 monkeys. As many as 670 of these rare monkeys have been observed together when food is plentiful.
The study’s findings are described in detail in the Cell Press journal Current Biology.